Phosphate containing compounds are major ingredients of such industrial products as fertilizers, chemical reagents, pigments, etc. In most cases, such phosphates are produced by means of utilizing phosphoric acid reagent. Phosphoric acid is usually obtained by the treatment of phosphate minerals contained in various oxidic ores. Phosphate minerals are major constituents in ores such as apatite, phosphorite and pebble phosphates. Phosphate minerals may also occur as minor constituents in many other oxidic ores, for instance in dolomitic ores and similar alkaline earth metal carbonates, and are usually accompanied by quartz and other siliceous gangue minerals. In the above instances, the phosphate minerals need to be separated from other constituents of the ore and from the gangue, by a beneficiation process to yield a phosphate mineral concentrate. The phosphate mineral concentrate so obtained may subsequently be treated to produce phosphoric acid.
It is usual in a beneficiation process to first grind the ore to a suitable liberation size. Grinding may be wet or dry. Conventional benefication processes often include a step to remove particles of very small size from the ground ore before the ore is subjected to further beneficiation. The fine particles are usually referred to as slimes, and the removal of fine particles is usually termed desliming.
The actual size of the particles which are considered as slime depends on the composition of the minerals contained in the ore, the chemical and physical nature of the small particles, the various chemical reagents used in subsequent steps and the character of the mineral values which are retained in the slime. Thus slime separation and treatment will be governed by chemical, physical and economic considerations. In phosphate beneficiation processes, particle sizes less than generally 200 Tyler mesh are considered as slime.
The ground ore may undergo other conventional mineral beneficiation steps, such as for instance, magnetic separation before or after desliming. The insertion of such steps are dictated by the nature of the ore and economic considerations only.
Froth flotation separation commonly forms a part of a beneficiation process. The ground ore is usually made into an aqueous slurry and added to the slurry are chemical reagents which may be preferentially adsorbed by particles containing value minerals. The chemical reagents adsorbed on the surface of particles will either enhance wetting by water or diminish wetting of certain particles. These chemical reagents are generally referred to as collector agents or depressant agents. Collector agents are chemical reagents which when adsorbed on the surface of a particle diminish the wetting of the particle by water. Depressant agents are those chemical reagents which usually enhance the wetting of particles. In a conventional froth flotation process air bubbles are introduced into the aqueous slurry. The air bubbles usually attach themselves to the non-wetted particles, thereby raising them to the top or froth of the slurry. The froth is usually skimmed off and/or is channelled off in an overflow. The froth thus contains the concentrate of certain value minerals which have not been wetted by water as a result of interaction with reagents added in the flotation separation process. The particles wetted, on the other hand, tend to be depressed into the residue of the froth flotation process.
The froth flotation step is usually preceded by a conditioning step whereby reagents are added to the ore slurry in order to enhance the adsorption of depressing agents and collector agents onto the surface of the ore particles. A frother may also be added to the conditioned ore slurry to promote the generation of froth.
Conventional phosphate beneficiation may include two separate froth flotation step sequences. In the first step sequence, froth flotation is performed with a fatty acid collector to obtain a low grade phosphate product. The low grade product is then treated with an acid for the removal of the fatty acid reagent before the fraction so obtained may be subjected to a second froth flotation step sequence, utilizing an amine flotation reagent to float preferentially the gangue particles. U.S. Pat. No. 4,189,103 issued Feb. 19, 1980 to Lawver et al., describes such a complex phosphate beneficiation process which additionally includes several size separation and gravity separation steps. The process of U.S. Pat. No. 4,189,103 utilizes fatty acid flotation reagents in one of its stages and an amine froth flotation agent in another stage. In another patented process, U.S. Pat. No. 4,372,843 issued in Feb. 8, 1983 to Lawver et al., the pebble fraction obtained in the size separation is ground to a smaller size and then subjected to reverse flotation. In the reverse flotation the phosphate minerals are depressed into the underflow of the froth flotation cell. U.S. Pat. No. 4,372,843 utilizes a sulphonated fatty acid carbonate collector and a phosphate depressant.
In conventional direct phosphate froth flotation processes reagents are added for depressing quartz, dolomite and similar alkali metal carbonates to the tailing. A .dolomitic phosphate beneficiation process is described in U.S. Pat. No. 4,804,462 issued on Feb. 14, 1989 to Zheng-xing Gu et al. In that process the ore is subjected to several conditioning stages with a fatty acid and fuel oil reagent, and then to froth flotation steps utilizing humic acid as collector reagent.
Most conventional phosphate beneficiation processes are either very complex and therefore costly, or provide low phosphate recovery rates.
Another disadvantage of most conventional processes is that the slimes separated from the ground ore may not be treated economically for further phosphate recovery and are therefore discarded.
It has now been found that phosphate minerals may be separated in a relatively simple phosphate beneficiation process utilizing a novel phosphate collector agent.
The novel phosphate collector agent of the present invention comprises an oxidized intimate mixture of ingredients comprising initially:
i) 20-60% by weight of a fatty acid containing 12-36 carbon atoms in its hydrocarbon chain, PA1 ii) 5-25% by weight of a tall oil pitch, PA1 iii) 2.5-15% by weight of an amine derived from a plant, PA1 iv) 0-15% by weight of sarcosine, and additionally comprising, as the balance of said mixture, 20-72.5% by weight of one of the group consisting of a fuel oil and furnace oil.
The fuel oil or the furnace oil may be added to the mixture of ingredients either prior to oxidizing or subsequent to it.
The phosphate collector of this invention is added to the ground and deslimed phosphate containing ore which has been slurried in water. For best results the slurried ore is conditioned with a pH modifier, such as sodium carbonate or similar conventional pH adjusting reagent. Other conventional conditioning agents, such as for example alkali metal silicates may be added prior to rougher and/or cleaner flotation stages. The conditioned ore slurry containing the phosphate collector of this invention is then subjected to froth flotation. The phosphate minerals contained in the ore are separated in the froth. The phosphate mineral concentrate so obtained may then be treated in process steps for further recovery.
It is an additional advantage of the present invention that the separated slimes may also be treated in a separate phosphate recovery process step utilizing the novel phosphate collector agent.